The present invention relates to a vehicle AC generator having a Landor rotator.
FIG. 7 to FIG. 11 show a configuration of a vehicle AC generator in the prior art, FIG. 7 is a sectional view of the generator, FIG. 8 is a perspective view of a rotor, FIG. 9 is a perspective view of a stator, FIG. 10 is a perspective view of a stator core, and FIG. 11 is an illustrative view of a relationship between the rotor cores and the stator core. In FIG. 7, 1 denotes a front bracket; 2, rear bracket; and 3, a stator put between the front bracket 1 and the rear bracket 2. As shown in FIG. 7, FIG. 9, and FIG. 10, the stator 3 consists of a stator core 4, and a three-phase stator coil 5 inserted in a slot 4a of the stator core 4.
In FIG. 7 and FIG. 8, 6 is a rotor which fixed onto a rotation axis 7 whose both ends are supported by the front bracket 1 and the rear bracket 2. The rotor 6 comprises a first rotor core 8, a second rotor core 9, a field coil 10 wound between both rotor cores 8 and 9, fans 11, 12 provided on the back surfaces of both rotor cores 8 and 9, a pulley 13 provided on the outside of the rotation axis 7 on the front bracket 1 side, and a slip ring 14 provided on the inside of the rotation axis 7 on the rear bracket 2 side to supply a current to the field coil 10. Then, 15 denotes a brush for supplying a current to the slip ring 14; 16, a brush holder for holding the brush 15; 17, a rectifier for rectifying the AC output of the stator coil 5; and 18, a regulator for controlling the output voltage of the stator coil 5 by adjusting the current of the field coil 10.
Also, as shown in FIG. 8 and FIG. 11, a plurality of almost trapezoidal pole pieces 8a, 9a whose width is reduced toward a tip portion in the rotation direction are formed on the first rotor core 8 and the second rotor core 9 respectively so as to oppose to an inner diameter surface of the stator core 4. Thee pole pieces 8a, 9a are arranged to engage alternatively via a predetermined clearance, and magnetized alternatively to the N pole and the S pole. In addition, in order to suppress the electromagnetic sound by smoothing the magnetic flux distribution in the air gap, chamferings 8b, 9b are provided on corner portions between outer surfaces of the pole pieces 8a, 9a opposing to the stator core 4 and both end surfaces in the rotation direction.
In the vehicle AC generator constructed as above in the prior art, the rotor 6 is driven by the internal combustion engine via pulley 13 while the current is supplied from a battery (not shown) mounted in the vehicle to the field coil 10 via the brush and the slip ring 14, the rotor 6 generates a rotating magnetic field, then the three-phase AC voltage is generated in the stator coil 5 by this rotating magnetic field, and then this voltage is rectified by the rectifier 17 to be supplied lo a load (not shown).
In this manner, when the generator is in the running state and the load is composed or a resistance load, an output current of the generator can be expressed by the following equation.
I=KBDxc3x971/L/{l+[(R+r)/xcfx89L]2}xc2xdxe2x80x83xe2x80x83(1)
where K is a constant, B is a magnetic flux density in an air gap, D is an outer diameter of the rotor 6, l is a conductor length of the stator coil 5, L is a self-inductance of the stator coil 5, R is a resistance value of the load, r is a resistance value of the stator coil 5, and xcfx89 is an angular velocity of the rotating magnetic field.
In Eq. (1), parameters other than the angular velocity xcfx89 are decided based on design specifications of the generator and load conditions. Then, if the number of revolution of the generator, i.e., xcfx89 is increased, the output current characteristic exhibits the saturation characteristic because of the influence of the reactance xcfx89L which is also Increased together with xcfx89. The current Is in this saturation state can be expressed by
Isxe2x88x9dBDxc3x971/Lxe2x80x83xe2x80x83(2)
Accordingly, it is understood that, in order to increase the output current at the time of high speed rotation of the generator, i.e., the saturation current Is to obtain the higher output, the magnetic flux density B, the diameter D of the rotor , and the conductor length l of the stator coil 5 must be increased and also the self-inductance L of the stator coil 5 rust be reduced.
However, in order to decrease the inductance L, the number of turns of the stator coil 5 must be reduced. But this is not effective in increasing the output current because such reduction results in reduction of the conductor length l of the stator coil 5 at the same time. In order to increase the output while avoiding the increase in sire of the generator, i.e., without the change of the D in above Eq. (2), there is no way to increase the magnetic flux density D. However, in such generator, tile magnetic flux density B in the loaded condition is extremely reduced rather than the magnetic flux density B in no load condition because of the armature reaction caused by the output current Is. Therefore, the increase of the magnetic flux density B in the loaded condition, i.e., the suppression of the armature reaction is the necessary condition to increase the output current of the generator.
Further, in the low speed revolution of the generator, the corresponding number of revolution is needed to increase the generation voltage up to a predetermined value (battery voltage), and also the output cannot be obtained unless the exciting current value flowing into the field coil 10 is compensated. Therefore, the output current of the generator does not rise unless the number of revolution comes up to the predetermined number of revolution. Since the number of revolution required for the rising of the output current is in inverse proportion to the generated voltage of the stator coil 5, the generated voltage of the stator coil 5 must be increased to lower the rising number of revolution required for the output current in the low speed revolution. The generated voltage E can be expressed by
Exe2x88x9dBlv=Blxcfx89D/2xe2x80x83xe2x80x83(3)
As given in Eq. (3), the magnetic flux density B must also be increased to improve the output characteristic in the low speed revolution. Here the magnetic flux density B corresponds to the magnetic flux density in the air gap formed between the pole pieces 8a, 9a in the magnetic path indicated by the magnetic flux "PHgr" in FIG. 7 and the stator core 4. Thus, the reduction of the magnetic reluctance in the air gap leads to the increase of the output in the low speed revolution.
Since the vehicle AC generator is driven by the internal combustion engine at a predetermined speed increasing ratio, the available range of the number of revolution extends from 0 to 18,000 rpm. In particular, the improvement of the output characteristic is requested in the neighborhood of the number of revolution of the generator of about 1,500 rpm, which corresponds to the idling number of revolution of the internal combustion engine, and the number of revolution of the generator of about 6,000 rpm, which corresponds to the normal running state of the vehicle. Because the number of revolution at which the above output current Is becomes the saturation state is about 5,000 rpm, such configuration must be employed as the generator that importance of the increase of the output current Is in the saturation state and the increase of the output current in the idling operation by lowering the number of revolution at the rising of the output current are considered.
To increase the magnetic flux density B in the air gap, as described above, is necessary for the reduction of the number of revolution of the rising output current, i.e., the improvement of the output characteristic in the low speed revolution. This increase can be attained by reducing the magnetic reluctance in the air gap. However, if areas of the pole pieces 8a, 9a of the rotor 6 are increased to reduce the magnetic reluctance in the air gap, widths of the pole pieces 8a, 9a must be increased in the rotation direction to avoid the increase in size of the generator. As a result, clearances between neighboring pole pieces 8a and 9a are reduced to then increase the leakage magnetic flux, and thus this imposes the limitation on the improvement of the output characteristic. Moreover, since such increase of the areas of the pole pieces results in the increase of the demagnetizing force due to the armature reaction, the output current Is in the saturation state cannot achieve the sufficient output improvement, so that it is extremely difficult to improve the output from the low speed range to the high speed range.
The present invention has been made to overcome such subjects, and it is an object of the present invention to provide a vehicle AC generator capable of improving the output characteristics in the full rotation range from the low speed range equivalent to the idling rotational speed to the output current saturation range as the normal using range.
A vehicle AC generator according to the present invention comprises a stator core having a stator coil; a first rotor core and a second rotor core provided on an inner diameter side of the stator core to be fixed to a rotation axis; a field coil for magnetizing the first rotor core and the second rotor core; and a plurality of pole pieces provided on the first rotor core and the second rotor core to extend in an axis direction of the rotation axis, and arranged to engage alternatively with each other via a predetermined clearance, and provided to oppose to an inner diameter surface of the stator core via a predetermined clearance; wherein the poles pieces are formed into an almost trapezoidal shape to reduce a width toward its tip portion in a rotation direction, and a skew angle against the axis direction of both side surfaces of the pole pieces in a rotation direction is set small on a root side and also set large on a tip side.
Also, the skew angle of both side surfaces of the pole pieces is set small in angle in about ⅔ of a total length between the root side to the tip side from the root side and set large in angle in about ⅓ on the tip side.
Further, chamferings are formed on corner portions between an outer surface opposing to the stator core of the pole piece and both side surfaces in the rotation direction.
Furthermore, a rotation direction wide dimension of the chamferings formed on corners between an outer surface of the pole piece and both end surfaces in the rotation direction is set small on the root side of the pole piece and is set large on the tip side.
Moreover, a radial direction depth of the chamferings formed on corners between an outer surface of the pole piece and both end surfaces in a radial direction is set small on the root side of the pole piece and is set large on the tip side.